Implantable heart stimulator with electrodes for an infection control current

ABSTRACT

An implantable heart stimulator has an electrically conductive housing containing a pulse generator, with an electrode lead connected to the housing. The electrode lead has a proximal portion extending substantially from the housing to a location, after implantation, which is beyond the entry of the lead into the venous system and before the entry of the lead into the superior vena cava. A current source supplies an infection control current between the housing and an electrically conductive surface on the exterior of the proximal portion of the electrode lead, for counteracting bacterial growth. The housing may have a header to which the electrode lead is connected, in which case the header is provided with an electrically conductive surface as well, which can serve as an electrode for the infection control current.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an infection control apparatus for animplantable heart stimulator of the type having a pulse generator fordelivering electric stimulation pulses to a patient's heart through alead connectable to the pulse generator, through a connector top on apulse generator housing, the pulse generator housing being electricallyconductive.

2. Description of the Prior Art

Implantable heart stimulator pocket infection is a severe complicationwhich often ends up in explantation of the stimulator. The reasontherefor is that conventional treatment with antibiotics cannoteradicate the infection. This seems to depend on the circumstance thatthe bacteria live in a biofilm formed around the exterior surfaces ofthe implanted stimulator, which film blocks antibiotics. The bacteriamay also live passively on a very low metabolism and can therefore notbe treated successfully by antibiotics.

A method of enhancing the effect of antibiotics by applying anelectrical field across the bioflim is described in U.S. Pat. No.5,312,813. This method is based on findings by J. W. Costerton et. al.Their studies have shown that the infection can be completely cured andno explantation has to take place by applying an electric field or asmall current across the biofilm during antibiotic treatment, cf. alsoASAIO Journal 1992, p. M174–M178, Khoury et. al, “Prevention and Controlof Bacterial Infections Associated with Medical Devices”, andAntimicrobial Agents and Chemotherapy, Vol. 38, No. 12, December 1994,p. 2803–2809, Costerton et. al., “Mechanism of Electrical Enhancement ofEfficacy of Antibiotics in Killing Biofilm Bacteria”. In these studies,generally, a low electric current of the order of 15–400 μA/cm² isapplied onto the infected surface while immersed in a buffer withantibiotics. In the most successful studies a total killing ofmicroorganisms was reported after only 8 hours of current and antibiotictreatment—tobramycin 2.5 mg/l, 15–400 μA/cm², during 8 h. This effecthas been termed “the bioelectric effect”.

These studies suggest that the electric field needs to be applied inclose proximity to the infected implant. A possible explanation for theobserved effect is that electrochemically generated products are neededfor the bioelectric effect to occur. At the titanium surface, titaniumbeing normally used in heart stimulator housings, the followingelectrochemical processes take place.

At the anode:2H₂O→O₂+4H⁺+4e ⁻  1)2Cl⁻.→Cl₂+2e ⁻  2)Ti+2H₂O→TiO₂+4H⁺+4e ⁻  3)

At the cathode:O₂+2H₂O+4e ⁻→4OH⁻  1)2H₂O+2e ⁻→H₂+2OH⁻  2)

It is supposed that primarily the produced oxygen and chloride gaseshave an influence on the biofilm attached to the surface. It is alsosupposed that the fact that the pH-value is lowered at the anode andincreased at the cathode is significant for the influence and viabilityof the biofilm.

An infection that is initiated in the stimulator pocket will also oftenstart to spread along the lead. The polymer surface of the lead may be asubstrate for the bacteria and makes it easy for the bacteria to attach.At the time when a pocket infection is clinically manifested, in manycases the infection has already spread some distance from the stimulatorpocket along the lead.

As the bioelectric effect is concentrated to parts in conjunction withor in close proximity to conducting surfaces of the implant, it is onepurpose of the present invention to extend these conducting activesurfaces.

SUMMARY OF THE INVENTION

The above object is achieved in accordance with the present invention inan implantable stimulator having a pulse generator with an electricallyconductive housing, and an electrode lead connected to the pulsegenerator having a proximal portion which extends from the housing to alocation, after implantation, situated between entry of the electrodelead into the venous system and before entry of the electrode lead intothe superior vena cava, this proximal portion having an electricallyconductive exterior surface, and a current source which supplies aninfection control current between the metallic housing and theelectrically conductive exterior surface of the proximal portion of theelectrode lead.

The housing may be provided with a connector top or header, having asocket for making mechanical and electrical connection with theelectrode lead, with at least a portion of the exterior surface of thisconnector top being electrically conductive. If a connector top of thistype is present, at least two electrodes are formed from among themetallic housing, the electrically conductive portion of the exterior ofthe connector top, and the electrically conductive exterior surface ofthe proximal portion of the electrode lead, which are supplied with theinfection control current by the current source.

As discussed above the bioelectric effect is limited to conductingsurfaces of the implanted device or to the immediate proximity thereof.With the present invention a design is obtained which makes it possibleto extend the bioelectric effect to surfaces of an implanted heartstimulator, which conventionally are non-conducting. The heartstimulation may be a pacemaker or a cardioverter-defibrillator (ICD). Bymaking exterior surfaces of the proximal part of the lead and theconnector top (if present) electrically conductive, all exteriorstimulator surfaces located within the subcutaneous implant pocket and apart of the lead extending from the pocket are electrically conductive.By adapting these electrically conductive surfaces to form at least twoseparate electrodes and providing a current source to supply an electricinfection control current between these electrodes, all exteriorsurfaces will be permeated by current, and the bioelectric effect willbe extended to all surfaces within the pocket and also to the exteriorsurface of the proximal part of the lead. By making the normallynon-conducting surfaces of the connector top and the lead electricallyconducting, not only effective treatment of infections within the pocketis possible, but spreading of the infection from the pocket along thelead is prevented. The lead will in this way benefit from thebioelectric effect and thus bacteria are prevented from reaching theendocardium giving rise to endocarditis.

In an embodiment of the apparatus according to the invention anelectrically conducting polymer is applied on said exterior surfaces ofthe proximal part of said lead and said possible connector top. In thisway traditionally non-conducting surfaces of a heart stimulator are madeelectrically conductive. An example of a polymer suitable for thispurpose is an electrically conducting polymer marketed under thetrademark ELASTOSIL.

In another embodiment of the apparatus according to the invention anelectrically conducting coil is applied around the proximal part of thelead. In this way the proximal part of the lead not only is madeelectrically conductive but also the wear resistance of the lead isimproved.

In another embodiment of the apparatus according to the invention theexterior surfaces of the proximal part of the lead and of said connectortop (if present) are treated by ion implantation technology or so-calledIon-Beam-Assisted-Deposition. This technique is especially well suitedfor making stimulator connector tops or headers of epoxy electricallyconductive.

Other possible technologies to make a surface conducting are PhysicalVapor Deposition, PVD, or Chemical Vapor Deposition, CVD or anysputtering process.

It has been found that oxide layers, especially titanium oxide layersbut also other metal oxide layers may be formed when such metals areused in the DC current environment which exists in conjunction with thepresent invention. These oxide layers may cause an uneven currentdistribution possibly detrimental to the infection control effect. Thecurrent may also be lowered due to increased impedance caused by theoxide layer to a point at which the effect on bacteria in the biofilm isno longer effective. The formation of such oxide layers is avoided,according to an embodiment of the apparatus according to the invention,by coating the generator housing and other metallic surfaces that maybecome oxidized due to the DC current with one of the metals platinum,palladium or iridium or any other metal with similar electrochemicalcharacteristics or an alloy of these metals.

In a further embodiment of the apparatus according to the invention thecurrent source is formed by an electric pulse generator battery. Thus incase of heart stimulators, like pacemakers or ICDs, having their ownenergy source, no external source will be required.

In another embodiment of the apparatus according to the invention aninductive coupling arrangement provided to inductively couple anexternally located current source to the electrodes thereby avoidingloading of the internal battery.

In a version of this embodiment of the apparatus according to theinvention the inductive coupling arrangement is a single layer inductivecoil attached to the outer surface of the pulse generator housing andelectrically connected to the electrodes or an inductive coil positionedinside the pulse generator housing and electrically connected to theelectrodes. Such single layer coils, which are manufactured preferablyby screen printing, will not require much space and will consequentlycontribute to a compact stimulator construction. A rectifier isconnected between the coil and one of the electrodes to supply a DCcurrent to the electrodes. Such a coil might also be used as a telemetrycoil.

In another embodiment the connector top and the pulse generator housingare adapted to be in mechanical contact with transcutaneously insertedneedles that inject the infection control current from a current sourcelocated outside the patient's body.

The present invention also relates to a heart stimulator having a pulsegenerator for delivering electric stimulation pulses to a patient'sheart through a lead, connectable to the pulse generator, through aconnector top on a pulse generator housing, the pulse generator housingbeing electrically conductive, and having an infection control currentgenerating apparatus as disclosed above.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a heart stimulator with a leadprovided with a coil at a proximal portion thereof, in accordance withthe invention.

FIG. 2 is illustrates an embodiment of the invention with a pulsegenerator housing serving as a first electrode and at least one of theproximal portion of an electrode lead, and the connector top, serving asa second electrode, for the infection control current.

FIG. 3 is a schematic illustration of a heart stimulator in accordancewith the invention with a surface mounted coil on the exterior of thestimulator housing for inductively connecting an external current sourcefor the infection control current.

FIG. 4 illustrates an embodiment of the invention wherein the infectioncontrol current is delivered from an external current source viatranscutaneous electrodes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the apparatus according to the invention, the proximal part of thelead, which extends to a position after implantation of the leadsituated beyond the entry into the venous system and before the entryinto the superior vena cava, is made electrically conductive. This canbe realized in several different ways. Thus the proximal part can bemade electrically conductive e.g. applying an electrically conductingpolymer on its surface or by other techniques, previously described suchas ion implantation technology, Ion-Beam-Assisted-Deposition (IBAD). InFIG. 1 another example of making a proximal lead part electricallyconductive is shown.

FIG. 1 shows schematically an implantable heart stimulator 2 having aconnector top 4 to which a lead 6 is connected. The proximal part of thelead 6 is made electrically conductive by wrapping a metallic coil 8around this part of the lead. The metallic coil 8 will also improve thewear resistance of the lead 6.

The connector top or header 4 is often made of epoxy and IBAD or any ofthe previously described techniques is suitable for making such aconnector top conductive.

FIG. 2 shows an embodiment with an electrically conductive stimulatorhousing, an electrically conductive connector top 12 and a lead 14 withan electrically conductive proximal part 16. The pulse generator housing10, which normally is made of titanium, serves as a first electrode andis isolated from the connector top 12 and the lead 14, which are forminga second electrode. The electrically conductive proximal part 16 of thelead 14 extends to a position which after implantation of the lead issituated beyond the entry into the venous system and before the entryinto the superior vena cava. With this embodiment it is insured that allexterior surfaces of the implanted stimulator receive adequate therapyby connecting a current source (not shown in FIG. 2) in any suitable wayto the electrodes.

The pulse generator housing, connector top and proximal part of the leadcan be divided into two separate electrodes in a number of other ways.Thus, e.g. the pulse generator housing and connector top can form oneelectrode, while the proximal part of the lead forms the other. Othercombinations are apparent. It is important, however, that the electrodesare designed such that the current distribution for the bioelectriceffect is as uniform as possible across the exterior surfaces.

FIG. 3 shows schematically an embodiment for generating current forelectric infection control by electromagnetic induction. Thus a superthin surface mounted coil 18 is attached to the exterior surface of thestimulator housing 20. This coil 18 can be manufactured by e.g. screenprinting. A polymeric isolation film 22 is provided to electricallyisolate the coil 18 from the stimulator housing 20.

One end 24 of the coil 18 is electrically connected to the housing 20,while the other end is connected to a diode 26 integrated in the epoxyconnector head 28. The diode 26, in its turn, is connected to a counterelectrode 30 at the external surface of the connector head 28.

By applying a high frequency electromagnetic field by an external energysource located in the proximity of the stimulator, a current will begenerated in the coil 18. The diode 26 will allow current in only onedirection and thus permit the electrochemical processes necessary forthe bioelectric effect to occur. As an alternative, the coil can beplaced inside the stimulator housing. One end of the coil is thenconnected to the stimulator housing, whereas the other end of the coilis connected via a diode to an external counter electrode, preferablyintegrated in the epoxy connector head.

FIG. 4 shows schematically the implanted pulse generator in the patient.The conductive connector top 4 and the proximal conductive portion 8 ofthe lead 6 form one electrode and the casing 2 of the pulse generatorform the other electrode. The external infection control current source31 is connected to the conductive connector top and the pulse generatorcasing via transcutaneous electrodes 29,30

Although modifications and changes may be suggested by those skilled inthe art, it is the invention of the inventors to embody within thepatent warranted heron all changes and modifications as reasonably andproperly come within the scope of their contribution to the art.

1. An implantable heart stimulator comprising: a pulse generator and anelectrode lead connected thereto for delivering electrical stimulationpulses to a heart of a patient, said pulse generator having anelectrically conductive housing, said housing comprising a connectorheader in which said electrode lead is mechanically and electricallyconnected; said electrode lead having a proximal portion which, afterimplantation of said electrode lead, is configured to extendsubstantially from the housing to a location situated beyond entry ofthe electrode lead into the venous system and before entry of theelectrode lead into the superior vena cava, said proximal portion havingan exterior with an electrically conductive surface; and a currentsource for supplying an infection control current between said housingand said electrically conductive surface of said proximal portion ofsaid electrode lead for counteracting bacterial growth at least on anexterior of said housing, said connector header having an exteriorsurface that is entirely electrically conductive and is in a flow pathof said infection control current.
 2. An implantable heart stimulator asclaimed in claim 1 wherein at least one of said electrically conductivesurface on the exterior of said proximal portion of said electrode leadand said electrically conductive surface on said exterior of saidconnector header is formed by an electrically conducting polymer.
 3. Animplantable heart stimulator as claimed in claim 1 wherein at least oneof said electrically conductive surface on the exterior of said proximalportion of said electrode lead and said electrically conductive surfaceon said exterior of said connector header is formed by an ionimplantation.
 4. An implantable heart stimulator as claimed in claim 1wherein at least one of said electrically conductive surface on theexterior of said proximal portion of said electrode lead and saidelectrically conductive surface on said exterior of said connectorheader is formed by ion beam assisted deposition.
 5. An implantableheart stimulator as claimed in claim 1 wherein at least one of saidelectrically conductive surface on the exterior of said proximal portionof said electrode lead and said electrically conductive surface on saidexterior of said connector header is formed by a coating processselected from the group consisting of vapor deposition and sputtering.6. An implantable heart stimulator as claimed in claim 1 wherein saidelectrically conductive surface on said exterior of said connectorheader is electrically isolated from said electrically conductivesurface on said exterior of said proximal portion of said electrodelead.
 7. An implantable heart stimulator as claimed in claim 1 whereinsaid conductive surface at the exterior of said proximal portion of saidelectrode lead is formed by an electrically conductive coil.
 8. Animplantable heart stimulator as claimed in claim 1 wherein said housinghas an exterior coated with a metal selected from the group consistingof platinum, palladium, indium, platinum alloys, palladium alloys andindium alloys.
 9. An implantable heart stimulator as claimed in claim 1wherein said electrically conductive surface at said exterior of saidproximal portion of said electrode lead is electrically isolated fromsaid housing.
 10. An implantable heart stimulator as claimed in claim 1wherein said current source comprises a battery contained in saidhousing, which also supplies power to said pulse generator.
 11. Animplantable heart stimulator comprising: a pulse generator and anelectrode lead connected thereto for delivering electrical stimulationpulses to a heart of a patient, said pulse generator having anelectrically conductive housing; said electrode lead having a proximalportion which, after implantation of said electrode lead, is configuredto extend substantially from the housing to a location situated beyondentry of the electrode lead into the venous system and before entry ofthe electrode lead into the superior vena cava, said proximal portionhaving an exterior with an electrically conductive surface; and anextracorporeal current source, and an inductive coupling arrangement toinductively couple said extracorporeal current source with said housingand said electrically conductive surface on said exterior of saidproximal portion of said electrode lead supplying an infection controlcurrent between said housing and said electrically conductive surface ofsaid proximal portion of said electrode lead for counteracting bacterialgrowth at least on an exterior of said housing.
 12. An implantable heartstimulator as claimed in claim 11 wherein said inductive couplingarrangement comprises a thin inductive coil attached at an outer surfaceof said housing, and electrically connected to said housing and to saidelectrically conductive surface on said exterior of said proximalportion of said electrode lead.
 13. An implantable heart stimulator asclaimed in claim 11 wherein said inductive coupling arrangementcomprises a thin inductive coil disposed inside of said housing, andelectrically connected to said housing and to said electricallyconductive surface on said exterior of said proximal portion of saidelectrode lead.
 14. An implantable heart stimulator as claimed in claim11 wherein said inductive coupling arrangement includes a diode forproducing a d.c. current as said infection control current.
 15. Animplantable heart stimulator as claimed in claim 11 wherein saidinductive coupling arrangement includes transcutaneous electrodesconnected between said extracorporeal current source and said housingand said electrically conductive surface on said exterior of saidproximal portion of said electrode lead.
 16. An implantable heartstimulator comprising: a pulse generator which generates electricalstimulation pulses; an electrically conductive housing containing saidpulse generator and having a connector header; an electrode leadmechanically and electrically connected in said header, and therebyconnected to said pulse generator, for delivering said stimulationpulses to a heart of a patient; said header having an exterior surfacethat is entirely electrically conductive; said electrode lead having aproximal portion extending substantially from said housing to alocation, after implantation of said electrode lead, adapted to besituated beyond entry into the venous system and before entry into thesuperior vena cava, said proximal portion having an exterior with anelectrically conductive surface thereon; a current source which suppliesan infection control current in a flowpath including at least two ofsaid housing, said electrically conductive surface on said exterior ofsaid header and said electrically conductive surface on said exterior ofsaid proximal portion of said electrode lead, to counteract bacterialgrowth at least one an exterior of said housing; and at least one ofsaid electrically conductive surface on the exterior of said proximalportion of said electrode lead and said exterior electrically conductivesurface of said connector header being formed by an electricallyconducting polymer.
 17. An implantable heart stimulator as claimed inclaim 16 wherein said conductive surface at the exterior of saidproximal portion of said electrode lead is formed by an electricallyconductive coil.
 18. An implantable heart stimulator as claimed in claim16 wherein said housing has an exterior coated with a metal selectedfrom the group consisting of platinum, palladium, indium, platinumalloys, palladium alloys and indium alloys.
 19. An implantable heartstimulator as claimed in claim 16 wherein said electrically conductivesurface at said exterior of said proximal portion of said electrode leadis electrically isolated from said housing.
 20. An implantable heartstimulator as claimed in claim 16 wherein said current source comprisesa battery contained in said housing, which also supplies power to saidpulse generator.
 21. An implantable heart stimulator as claimed in claim16 wherein said current source is an extracorporeal current source, andwherein said apparatus comprises an inductive coupling arrangement toinductively couple said extracorporeal current source with said housingand said electrically conductive surface on said exterior of saidproximal portion of said electrode lead.
 22. An implantable heartstimulator as claimed in claim 21 wherein said inductive couplingarrangement comprises a thin inductive coil attached at an outer surfaceof said housing, and electrically connected to said housing and to saidelectrically conductive surface on said exterior of said proximalportion of said electrode lead.
 23. An implantable heart stimulator asclaimed in claim 21 wherein said inductive coupling arrangementcomprises a thin inductive coil disposed inside of said housing, andelectrically connected to said housing and to said electricallyconductive surface on said exterior of said proximal portion of saidelectrode lead.
 24. An implantable heart stimulator as claimed in claim21 wherein said inductive coupling arrangement includes a diode forproducing a d.c. current as said infection control current.
 25. Animplantable heart stimulator as claimed in claim 21 wherein saidinductive coupling arrangement includes transcutaneous electrodesconnected between said extracorporeal current source and said housingand said electrically conductive surface on said exterior of saidproximal portion of said electrode lead.
 26. An implantable heartstimulator comprising: a pulse generator which generates electricalstimulation pulses; an electrically conductive housing containing saidpulse generator and having a connector header; an electrode leadmechanically and electrically connected in said header, and therebyconnected to said pulse generator, for delivering said stimulationpulses to a heart of a patient; said header having an exterior surfacethat is entirely electrically conductive surface; said electrode leadhaving a proximal portion extending substantially from said housing to alocation, after implantation of said electrode lead, adapted to besituated beyond entry into the venous system and before entry into thesuperior vena cava, said proximal portion having an exterior with anelectrically conductive surface thereon; a current source which suppliesan infection control current in a flowpath including at least two ofsaid housing, said electrically conductive surface on said exterior ofsaid header and said electrically conductive surface on said exterior ofsaid proximal portion of said electrode lead, to counteract bacterialgrowth at least one an exterior of said housing; and at least one ofsaid electrically conductive surface on the exterior of said proximalportion of said electrode lead and said exterior electrically conductivesurface of said connector header being formed by an ion implantation.27. An implantable heart stimulator comprising: a pulse generator whichgenerates electrical stimulation pulses; an electrically conductivehousing containing said pulse generator and having a connector header;an electrode lead mechanically and electrically connected in saidheader, and thereby connected to said pulse generator, for deliveringsaid stimulation pulses to a heart of a patient; said header having anexterior surface that is entirely electrically conductive surface; saidelectrode lead having a proximal portion extending substantially fromsaid housing to a location, after implantation of said electrode lead,adapted to be situated beyond entry into the venous system and beforeentry into the superior vena cava, said proximal portion having anexterior with an electrically conductive surface thereon; and a currentsource which supplies an infection control current in a flowpathincluding at least two of said housing, said electrically conductivesurface on said exterior of said header and said electrically conductivesurface on said exterior of said proximal portion of said electrodelead, to counteract bacterial growth at least one an exterior of saidhousing; and at least one of said electrically conductive surface on theexterior of said proximal portion of said electrode lead and saidexterior electrically conductive surface of said connector header beingformed by ion beam assisted deposition.
 28. An implantable heartstimulator comprising: a pulse generator which generates electricalstimulation pulses; an electrically conductive housing containing saidpulse generator and having a connector header; an electrode leadmechanically and electrically connected in said header, and therebyconnected to said pulse generator, for delivering said stimulationpulses to a heart of a patient; said header having an exterior surfacethat is entirely electrically conductive surface; said electrode leadhaving a proximal portion extending substantially from said housing to alocation, after implantation of said electrode lead, adapted to besituated beyond entry into the venous system and before entry into thesuperior vena cava, said proximal portion having an exterior with anelectrically conductive surface thereon; and a current source whichsupplies an infection control current in a flowpath including at leasttwo of said housing, said exterior electrically conductive surface ofsaid header and said electrically conductive surface on said exterior ofsaid proximal portion of said electrode lead, to counteract bacterialgrowth at least one an exterior of said housing; and at least one ofsaid electrically conductive surface on the exterior of said proximalportion of said electrode lead and said exterior electrically conductivesurface of said connector header being formed by a coating processselected from the group consisting of vapor deposition and sputtering.29. An implantable heart stimulator comprising: a pulse generator whichgenerates electrical stimulation pulses; an electrically conductivehousing containing said pulse generator and having a connector header;an electrode lead mechanically and electrically connected in saidheader, and thereby connected to said pulse generator, for deliveringsaid stimulation pulses to a heart of a patient; said header having anexterior surface that is entirely electrically conductive; saidelectrode lead having a proximal portion extending substantially fromsaid housing to a location, after implantation of said electrode lead,adapted to be situated beyond entry into the venous system and beforeentry into the superior vena cava, said proximal portion having anexterior with an electrically conductive surface thereon; and a currentsource which supplies an infection control current in a flowpathincluding at least two of said housing, said exterior electricallyconductive surface of said header and said electrically conductivesurface on said exterior of said proximal portion of said electrodelead, to counteract bacterial growth at least one an exterior of saidhousing; and said electrically conductive exterior surface of saidconnector header being electrically isolated from said electricallyconductive surface on said exterior of said proximal portion of saidelectrode lead.